Morphology Evolution of a High-Efficiency PSC by Modulating the Vapor Process

The morphological quality of the photoactive layer is the key component affecting the performance metrics of a photovoltaic device. Therefore, fine adjustment of the crystallization dynamics is urgently required. By manipulating the amount of dimethyl sulfoxide (DMSO) remaining in the spin-coated perovskite films during the annealing treatment, an obvious morphological evolution arises. The crystallization kinetics is significantly altered due to the formation of intermediate phases and the variation of DMSO vapor pressure via producing the semienclosed space with a covering. On the one hand, the obviously formed intermediate phase MA₂ Pb₃ I₈ (DMSO)₂ retards the crystallization process. On the other hand, the DMSO vapor in the semienclosed space intrigues the recrystallization process and results in Ostwald ripening to produce large-aspect-ratio grains with fewer defect states, decreased carrier doping, and longer carrier lifetimes. Thus, nonradiative processes are greatly suppressed. Besides, combined with X-ray photoelectron spectroscopy measurement and the surface energy of MAI- and PbI-terminated surface model calculated by density functional theory, the defect states are identified and the causes of Pb⁰ defect states are explained. Using this strategy, a high power conversion efficiency of 20.09% is achieved based on MAPbI₃ photovoltaic solar cell, and the long-term ambient shelf and thermal stability are obviously improved.